The present invention relates to a variable valve system for varying the valve lifts of engine valves such as intake valves or exhaust valves in each cylinder of an internal combustion engine in accordance with engine operating conditions.
Various types of variable valve systems have been proposed for internal combustion engines. Japanese Laid-Open Patent Publication No. 2000-38910 (abbreviated as “JP2000-38910A”) and Japanese Laid-Open Patent Publication No. 2006-161586 (abbreviated as “JP2006-161586A”) disclose variable intake valve systems, each of which is configured to vary the valve lifts and working angles of two intake valves in each cylinder of the internal combustion engine. The variable intake valve system of JP2000-38910A includes a drive shaft rotated by a crankshaft of the engine, two drive cams integrally mounted on the drive shaft, two swing cams mounted on the intake valves, two valve lift mechanisms for converting rotational movements of the drive cams into swing movements of the swing cams so as to open and close the intake valves and two control mechanisms for controlling the operating positions of the valve lift mechanisms so as to vary the valve lifts and working angles of the intake valves according to engine operating conditions. The variable intake valve system of JP2006-161586A includes a drive shaft rotated by a crankshaft of the engine, a drive cam integrally mounted on the drive shaft, a valve lift mechanism for converting a rotational movement of the drive cam into a swing movement of the swing cam so as to open and close the intake valves and a control mechanism for controlling the operating position of the valve lift mechanism so as to vary the valve lifts and working angles of the intake valves according to engine operating conditions.